A. Technical Field
The present invention relates to a catalyst for purification of exhaust gases, a production process therefor, and a process for purification of exhaust gases. Particularly, the invention relates to: a catalyst for purification of exhaust gases which catalyst is excellent as a denitrification catalyst for removing nitrogen oxides (NOX) from exhaust gases and as a catalyst for removing poisonous organohalogen compounds, such as dioxins, from exhaust gases; a production process therefor; and a process for purification of exhaust gases.
B. Background Art
A selective catalytic reduction process that is called SCR process is conventional as a process that is practically used at present for removing nitrogen oxides from exhaust gases wherein the selective catalytic reduction process comprises the steps of: catalytically reducing the nitrogen oxides (which are contained in the exhaust gases) on a denitrification catalyst with reducing agents such as ammonia and urea; and thereby decomposing the nitrogen oxides into harmless nitrogen and water. In recent years, as environmental pollution due to nitrogen oxides (typified by acid rain) assumes worldwide serious proportions, efficiency enhancement in denitrification arts is demanded more and more.
In such circumstances, a denitrification catalyst comprising oxides of titanium and vanadium and oxides of such as molybdenum and tungsten (JP-B-028148/1978) and a denitrification catalyst comprising a titanium-silicon-binary oxide and oxides of metals such as vanadium, tungsten, and molybdenum (JP-B-030532/1982) were put to practical use and are widely used at present.
All these catalysts have excellent ability to remove nitrogen oxides and low ability to oxidize sulfur oxides coexisting in exhaust gases, and further have excellent durability. However, it is favorable that catalysts which exhibit still higher performance emerge.
In addition, exhaust gases from incineration facilities for purification of industrial wastes and city wastes contain trace amounts of poisonous organohalogen compounds such as dioxins, PCB and chlorophenols. Particularly, the dioxins are so extremely poisonous as to have a serious influence on human bodies even if the quantities of the dioxins are very small. Therefore, a technology for removing the dioxins is desired to be developed as quickly as possible. A catalytic decomposition process is one of the most effective technologies and generally involves the use of catalysts comprising oxides of such as titanium, vanadium, tungsten and molybdenum, but, according to conditions of the exhaust gases, the performances of these catalysts cannot be said to be enough, therefore more enhancement of the catalytic performances is desired.